Inactivation of enzymes in beet cossettes prior to diffusion



llnited S tates fiatent INACTIVA'IION GF ENZYMES 1N BEET COSSETTES PRICET DL FUSION Harry S. Owens, Berkeley, Caiifi, assignor to United Statesof America as represented by the Secretary of Agriculture N0 Drawing.Application June 2, 1955, Serial No. 512,997

3 Claims. (Cl. 12743) (Granted under Title 35, U. S. Code (1952), sec.25%} A non-exclusive, irrevocable, royalty-free license in the inventionherein described, for all governmental purposes, throughout the world,with the power to grant sublicenses for such purposes, is hereby grantedto the United States of America.

This invention relates to sugar beets and has among its objects theprovision of processes for treating sugar beets whereby to facilitatethe recovery of sugar-bearing juice from the beets. A particular objectof the invention is the provision of processes for devitalizing thesugar beet tissue or inactivating the enzymes therein so that thesubsequent extraction of sugar from the tissue can be carried out moreeffectively and efiiciently. Particular advantages of the devitalizationprocess of this invention are:

(a) The capacity of the diffusion apparatus is increased.

(b) The devitalization is accomplished Without a dilution efiect on thesugar in the beets.

(c) The amount of non-sugars extracted during diffusion is decreased.

(d) The amount of fermentation which takes place during diffusion isdecreased.

(e) The diffusion juice contains a lower proportion of invert sugar,colloids, and colored materials than would normally be present.

Further objects and advantages of the invention will be obvious from thefollowing description.

In the production of sugar from sugar beets, the beets are first washedthen cut into strips known as cossettes. These cossettes are thensubjected to diilusion, that is, they are contacted with warm water tocause the sugar in the tissue to diffuse into the water. The diffusionmay be carried out batchwise or continuously. In the continuous processthe cossettes are carried through a series of about 20 cells by the useof drag chains or other mechanical devices. At the same time water ispassed through the cells in a direction countercurrent to the directionof cossette travel. The resulting liquor, known as raw juice, is thenpurified and subjected to evaporation and crystallization to obtain puresugar.

The difiusion process is a key step in the entire production and itseffectiveness depends upon many factors. For example, essentially allsugar in the beets must be extracted for the production to beeconomically sound. The extraction of sugar must be essentially completeyet the extraction of non-sugars must be kept at a minimum sinceincreased amounts of non-sugars introduce complications in the juicepurification steps necessitating use of more reagents, such as lime,carbon dioxide, filter aid, etc., and also increasing the amount ofnon-crystallizable sugar in the final molasses. Also the extraction ofsugar from the beets must be accomplished with a minimum amount of Waterbecause the water must eventually be evaporated and the production willnot be profitable unless the amount of water used is kept low so thatthe cost of evaporation will not be excessive. The diffusion ice:

process provides the raw material from which the crystalline sugar iseventually produced and every defect or disadvantage occurring duringdiffusion is passed along through the process and thus imposes a burdenon subsequent operations.

In order for the difiusion to be effective it is necessary that the beettissue be devitalized, that is, its viability must be destroyed. The rawbeet tissue is in a living state at least insofar as respiration andsimilar vital processes are concerned. In this viable state it thecossettes are contacted with water, diffusion of sugar from the beetcells into the water occurs at such an extremely slow rate as to benegligible for practical purposes. Thus in the viable state, the energyof the cells counteracts the osmotic pressure tending to cause diffusionof sugar out of the cells. It has been found, in laboratory experiments,that the rate of difiusion of sugar out of viable beet tissue is aboutone-eighth the rate of sugar diffusion out of devitalized beet tissue.

In commercial practice this devitalization (or scalding, ordenaturating, or blanching, as it may also he termed) is accomplished byinitially subjecting the raw cossettes to heated juice. Thus in acontinuous diflFuser, the first four or five cells in the diffusiontrain are provided with heaters so controlled that the juice withinthese cells is maintained at about C. The raw cossettes entering thesystem are at about air temperature (generally less than 20 C.) and theydo not actually reach the temperature of the liquid surrounding themuntil they leave the fourth or fifth cell. A scalding and diffusionsystem of this kind while expedient to use in practice, possesses manydisadvantages. In the first place the diffuser is not being used at itsactual capacity for diffusion. Thus the first four or five cells arebeing used partly as heat exchangers to heat the cossettes sufficientlyto devitalize them. Until the cossettes are brought up to thedevitalization temperature, diffusion is slow so that the total amountof difiusion which occurs in these cells is less than the amount whichwould take place where the cells being used solely for difiusion and notpartly for heat exchange and partly for diffusion. Another point is thatby maintaining the juice in four or five cells at about 85 C., the juiceis being unduly heated with the result that much colored material isdeveloped by reaction of reducing sugars with nitrogen compounds presentin the juice. These colored compounds add to the complexity ofsubsequently purifying the juice. Another point is that contacting thecossettes with juice at the relatively high temperature of 85 C. causesthe extraction of substantial amounts of colloidal materials (pectin,arabans, proteins, etc.) which interfere with purification of the juiceand crystallization of sugar. A further point is that considerablefermentation may take place. The raw cossettes contain a large microbialpopulation and these microbes multiply at a rapid rate particularly inthe first cell where the hot juice is cooled by the incoming coolcossettes. Conditions about the cossettes are favorable for microbialgrowth because of the warmth and the sugar and nitrogen nutrientspresent in the juice. Fermentation is a serious disadvantage since sugaris lost by being converted into lactic acid, acetic acid, carbondioxide, or into polysaccharides such as dextrans. The latter, being ofa glutinous, slimy nature, impede filtration and purification of thedifiusion juice.

It might be pointed out that in this known system wherein thedevitalization is efiectuated by contacting the raw cossettes withheated sugar-containing juice, the degree of devitalization cannot beincreased by raising the temperature of the juice which initiallycontacts the raw cossettes. If this were done, it would mean that thedevelopment of colored compounds (by interaction of reducing sugars andnitrogen compounds) would be greatly accelerated and also sugar sucrosewould be hydrolyzed to form invert sugar.

It has now been found that the disadvantages enumerated above can beminimized or even eliminated by a process which involves devitalizingthe raw cossettes by contacting them with heated moist air (or otherheated moist gas) prior to subjecting them to diffusion. Thus inaccordance with this invention the raw cossettes directly as obtainedfrom the slicers are contacted with heated moist air (or other gas) fora suificient period of time to cause essentially complete devitalizationor inactivation of the enzymes in the beet tissue. The so-treatedcossettes are then without delay subjected to conventional diffusionmployin empe at only high no o effective diffusion since heating tocause devitalization is now not nec ssary- The gaseous medium for thedevitalization is obtained, or e a pl by xin s am ith h i or by m xsteam with air at ordinary temperatures and then heating the mixture. Inany case the proportions of steam and air should be so adjusted that thegaseous m xture has a dry bulb temperature in the range from about 100to about 120 C. and a wet bulb temperature in the range from about 70 toabout 90 C. Instead of air, other gases may be used, for example,nitrogen, Waste gases from furnaces, etc. The use of the temperatures inthe above stated ranges produces several benefits. For example, by usinga dry bulb temperature of about 10.0 to 120 C., the temperature gradienttending to heat the raw cossettes is of a high order and as a result thetemperature of the cossettes is raised rapidly. A rapid rise in cossettetemperature is desirable since it means that the devitalization can becompleted in a few minutes. Rapid devitalization is not only desirablefrom an economic or efficiency standpoint but also is technologicallydesirable since it means that opportunity for undesirable reactions suchas degradation of cellular materials, synthesis of colored compounds,etc. is minimized. Further, by using a wet bulb temperature of 70 to 90C., it means that the cossette temperature cannot rise above this range.Thus the cossettes are wet and act in the same manner as the moist wickin a wet bulb thermometer. Thus no matter how long the contact ofcossettes and heated gas is maintained, the temperature of the cossettecannot rise above the wet bulb temperature of the gaseous medium. Thislimit on temperature rise is a very important benefit as itpreventsroverheating of the beet tissue. Over heating would lead todecomposition or degradation of cellular materials in the beet tissue,the decomposition products would be extracted from the beets in thesubsequent diffusion step and would interfere with the purificationprocess and the crystallization of sugar. The wet bulb temperature ofthe gaseous medium is therefore high enough to obtain essentiallycomplete devitalization of the beet tissue without causing anydeleterious eflfects. Also by using a moist gaseous-medium no watercondenses on the beets with the result that no dilution of the beetjuice in the beet cells occurs. Thus the gaseous medium has a lowrelative humidity as indicated by the large difference between the dryand wet bulb temperatures. When the gaseous medium is cooled by contactwith the cool cossettes, the relative humidity of the medium increasesbut not to such an extent that the gas becomes saturated with moisture.The net result is that all of the moisture present in the incomingstream of moist heated gaseous medium and any moisture evaporated fromthe cossettes remains as vapor in the gas stream and there is nocondensationof moisture.

Some of the advantages of the process of this invention are explained asfollows:

i (l) The capacity of the diffusion apparatus is increased beca se l vth cells n th dit usion t a are employe f c ua d ffus on; h s i n a y tocon ent prac e he ei the 1 2 1 e l s r e ma y to h t th Q settes. Sincethe capacity of the diffusion apparatus is increased, more beets can beprocessed in the same size difiusion apparatus resulting in substantialoperating economies. V

(2) Since the cossettes are treated with moist air and the moistureremains in the vapor phase there is no condensation of moisture andhence the sugar in the beets is not diluted. This means that the processof the invention does not lead to increased evaporation costs.

(3) After the cossettes have been devitalized by contact with the heatedmoist gas, they are extracted (subjected to diffusion) with water attemperatures optimum for diffusion of sugar from the cells into theliquid surrounding the cossettes. Such temperatures may be for examplefrom 50 to 70 C. Since the diffusion is conducted entirely at theserelatively low temperatures (as contrasted with temperatures of aroundC. in priorprocesses wherein the hot juice is used to scald the rawcossettes), the amount of nonfsugars extracted from the cossettes isdrastically reduced. In many cases the diffusion juice produced inaccordance with this invention will contain /2 to /2; as much colloidalmaterial as a conventional diffusion juice.

V r ual y no ierrnentation t e plac aus t cossettes are not contactedwith sugar-containing juice until the microbial population of thecossettes has been essentially destroyed. In the process of thisinvention, the raw cossettes are directly subjected to contact with amoist heated gas. The microorganisms being on the outide of thecossettes are rapidly decimated by the hot gas.

Then when the treated cossettes are subjected to diflusion and contactedwith sugar-containing juice, few microbes are present to causefermentation. This is in sharp contrast to conventional practice whereinthe raw cossettes loaded with microbial flora are directly contactedwith sugar-bearing juice; in such case conditions are ideal forfermentation to proceed at a rapid pace.

(5) The devitalization of the beet tissue by. direct contact with themoist hot gas takes place so rapidly that little opportunity is affordedfor the degradation of proteins, pectin, arabans, or for the hydrolysisof sucrose. This is in contrast to conventional practice wherein thejuice in the first 4 or 5 cells has to be maintained at tissue-devitalizing temperatures. In the usual difiusion system the, juice remains ineach cell for 3 minutes so that a total heating time of 12 to 15 minutesis involved which is conducive to the development of undesirableproducts such as degradation compounds of pectin, arabans, protein,sucrose, etc. which interfere with subsequent purification of the juiceor crystallization of sugar.

The devitalization n accordance with this invention can be accomplishedin many different types of equipment. The aim is primarily to providesome means for obtaining maximum contact of a stream of hot gas with allthe surfaces of a batch of cossettes being treated. Thus the cossettesmay be placed on a mesh tray while a current of the gas is passed overor preferably through them. T o insure good contact of gas and beets thetray or the cossettes themselves may be subjected to shaking, rotationor other form of movement to repeatedly expose different surfaces of thecossettes to the gas. T 0 promote rapid heating of the cossettes, it isalso preferred to employ a larger excess of hot gas over thattheoretically required and to apply it to the cossettes at highvelocity. The use of an excess of hot gas over that theoreticallyrequired to heat the beets to the proper temperature is advantageous notonly to enhance the rate'of heating but also to ensure that thetemperature of exhaust gas does not fall below its condensationtemperature. If this would happen, moisture would condense on the beetsand dilution would occur.

A convenient system of equipment for carrying out the devitalizationinvolves transporting the cossettes on an endless mesh belt through azone where they are subjected to a current of the heated moist gas. Thebelt conveyor may be arranged to receive the cossettes directly from thebeet slicers and to deliver the treated beets to the first cell of thedifiusion battery. Such a system is preferred as it is adapted to thecontinuous operation of the beet sugar line.

In contacting the raw cossettes with the moist hot gas, the time ofcontact is regulated to obtain essentially complete de-vitalization ofthe beet tissue, the treated cossettes then being removed from the zoneof heating. The proper time of contact will vary depending on manyfactors such as the properties of the beets, the degree of contactobtained between the gas stream and cossettes, the initial temperatureof the cossettes and temperature of the gas stream, etc. The proper timefor any particular set of circumstances can be determined by conductingthe process on a pilot batch of cossettes and withdrawing a sample ofthe cossettes from time to time and testing it for the presence ofactive enzymes. This may be done, for example, by cutting the cossettein half, placing a drop of 1% catechol solution on the cut surface andnoting whether or not a brown color develops. If no brown color developsthe cossette may be considered as devitalized as the enzyme systems havebeen inactivated. Other enzyme activity tests may be employed. Where thetreatment is performed under such conditions that the stream of hotmoist air makes good contact with most of the surface of the cossettesbeing treated, complete devitalization will be attained in a matter ofat most a few minutes, usually about from 1 to 5 minutes. Instead ofdetermining the optimum time for treatment by investigating thedisappearance of enzyme activity, one may ascertain the internaltemperature of the cossettes as by the use of a thermocouple or othertemperature measuring device small enough for insertion into a cossette.When the cossettes reach a temperature of at least 70 C., the tissue isproperly devitalized.

After the cossettes have reached the proper temperature to devitalizethe tissue, it is preferred that the cossettes be immediately subjectedto diffusion. By doing this the heating efiect is abruptly stopped sincethe cossettes come into contact with the relatively cool difiusionjuice.

The invention is further illustrated by the following example.

Twelve pounds of raw sugar beet cossettes were placed in a layer 1 inchdeep on a mesh tray and a hot moist air stream (dry bulb temp, 120 C.,wet bulb temp. 82 C.) was directed upwardly through the bed ofcossettes. This heating was continued for one minute. It was found thatthe beet tissue was devitalized as indicated by the absence of enzymeactivity in the tissue. Also the treated cossettes still weighed 12 lbs.indicating that there had occurred no uptake of water by the beets andtherefore no dilution of their sugar content.

Devitalized beets were subjected to diffusion with water at about C. Thesugar-containing diffusion juice was found to contain approximatelyone-third as much colloidal material precipitable at pH 2 as a standarddiffusion juice prepared in the usual way by directly subjecting the rawcossettes to diffusion using conventional scalding with hot diffusionjuice. The sugar yields in both cases were the same.

Having thus described the invention, what is claimed is:

1. A process for obtaining sugar from sugar beets which comprisessubjecting raw cut sugar beets to contact with a hot moist gas having adry bulb temperature about from 100 to 120 C. and a Wet bulb temperatureabout from 70 to C. to inactivate the enzyme in the beet tissue, anddirectly subjecting the so-treated beets to diffusion at a temperaturebelow that required to devitalize beet tissue whereby to obtain adiifusion juice having a reduced content of colloidal impurities.

2. The process of claim 1 wherein the difiusion is conducted at atemperature not higher than 70 C.

3. A process of obtaining a sugar-hearing difiusion juice having areduced content of colloidal impurities as compared with a normaldiffusion juice which comprises initially subjecting raw,freshly-prepared sugar beet cossettes to intimate contact with a currentof heated moist air having a dry bulb temperature about from to C. and awet bulb temperature about from 70 to 90 C. whereby to obtaindevitalization of the beet tissue in a period of time not over about 5minutes, immediately subjecting the so-treated beets to diffusion at atemperature of not over about 70 C. and separating the sugarbearingjuice of reduced colloidal content from residual beet pulp.

References Cited in the file of this patent UNITED STATES PATENTS304,013 Leblanc Aug. 26, 1884 934,965 Grabski Sept. 21, 1909 1,040,562Roberts Oct. 8, 1912 1,273,732 Bryant July 23, 1918 FOREIGN PATENTS1,497 Great Britain 1883 250,889 Great Britain Sept 2, 1926 274,131Great Britain Apr. 5, 1928 291,866 Great Britain June 11, 1928

1. A PROCESS FOR OBAINING SUGAR FROM SUGAR BEETS WHICH COMPRISES SUBJECTRAW CUT SUGAR BEETS TO CONTACT WITH A HOT MOIST GAS HAVING A DRY BULBTEMPERATURE ABOUT FROM 100 TO 120* C. AND A WET BULB TEMPERATURE ABOUTFROM 70 TO 90* C. TO INACTIVATE THE ENZYME IN THE BEET TISSUE, ANDDIRECTLY SUBJECTING THE SO-TREATED BEETS TO DIFFUSION AT A TEMPERATUREBELOW THAT REQUIRED TO DEVITALIZE BEET TISSUE WHEREBY TO OBTAIN ADIFFUSION JUICE HAVING A REDUCED CONTENT OF COLLOIDAL IMPURITIES.